The present invention relates to a demolition tool for breaking solid materials. It is particularly suitable for breaking rock or concrete in tunnelling, mining, demolishing and excavating applications.
A normal method of breaking rock comprises the steps of first drilling a number of holes with a percussive rock drilling machine and then loading the holes with explosives. The rock is then broken down by the forces created when the explosives are detonated. A percussive rock drilling machine cannot, in practice, be used for breaking down any considerable amounts of rock without the supplemental use of explosives, because of the limited energy delivered by each impact.
Another breaking method, which has so far been limited to demolition work, secondary breakage of rock and scaling, consists of using an impact hammer of the conventional jackhammer type which is larger, has a higher impact energy and is usually mounted on a backhoe or boom. In all impact hammers of this type, a reciprocating hammer is accelerated by compressed air or a pressurized liquid and strikes a chisel, which extends from the machine and is in contact with the material to be broken. The impact energy of such conventional impact hammers is limited by the maximum allowable impact velocity of the hammer, which is of the order of 10 m/s. An higher velocity would damage the contact surfaces of hammer and chisel too quickly.
One way of increasing the impact velocity, and thus the impact energy, consists in introducing a liquid cushion between the hammer and the working implement as described in U.S. Pat. No. 4,062,268. In this way the impact velocity can be increased to about 30 m/s. This means that the power to weight ratio is improved considerably since the impact energy is proportional to the square of the impact velocity.
Another prior art breaking device, which is suitable for demolition work, is described in U.S. Pat. No. 4,034,816. In this device the above mentioned velocity limitations are avoided because there is no impact between the hammer and a working implement. The hammer, or impactor, is of projectile type and is directly driven towards the material to be broken by combustion gas pressure.